1. Field of the Invention
This invention relates to an inductive type thin film magnetic head and a method for manufacturing the same, particularly a composite type thin film magnetic head comprising a writing inductive type thin film magnetic head and a reading magnetoresistive effective type thin film magnetic head which are stacked and supported by a substrate and a method for manufacturing the composite type thin film magnetic head.
2. Related Art Statement
Recently, with the development of surface recording density in hard disk devices, composite type thin film magnetic heads are required to have excellent characteristics.
Then, a composite type thin film magnetic head comprising an inductive type thin film magnetic head for writing and a magnetoresistive effective type thin film magnetic head for reading which are stacked on a substrate is suggested and practically used. Although as the reading magnetoresistive element, a magnetoresistive effective type thin film magnetic head using a normal anisotropic magnetoresistive (AMR) effect has been generally employed, magnetoresistive effective type thin film magnetic heads using a giant magnetoresistive (GMR), each head having a several times as large resistance variation as the AMR element, are developed. Moreover, magnetoresistive effective type tin film magnetic heads using a tunneling junction magnetoresistive (TMR) effect are developed.
In this specification, each of these AMR elements, GMR elements and TMR elements is generically called as a "magnetoresistive effective type thin film magnetic head" or a "MR reproducing element" in brief.
The use of the AMR element enables a surface recording density of several giga bits/inch.sup.2 to be realized, and the use of the GMR element enables the surface recording density to be more enhanced. Such a high surface recording density can realize a hard disk having a large capacity of more than 10G bites.
A height of a magnetoresistive reproducing element (MRH: MR Height) is a factor to determine a performance of a reproducing head composed of such a magnetoresistive reproducing element. The MR height is a distance between an air bearing surface and the end of the magnetoresistive reproducing element exposing to the air bearing surface. In a manufacturing process of a thin film magnetic head, a desired MR height is obtained by controlling the polishing amount of its air bearing surface when polishing the air bearing surface.
On the other hand, with the characteristics of the reproducing head being enhanced, the characteristics of the writing head is required to be developed. The development of the surface recording density requires an enhancement of a track density in a magnetic recording medium. Thus, a width of a write gap in an air bearing surface has to be narrowed to a submicron order from a several micron order, and for realizing it, a semiconductor processing technique is employed.
A throat height is a factor to determine a performance of a writing thin film magnetic head. The throat height is a distance to an edge of an insulating layer to electrically separate a thin film from its air bearing surface, which is desired to be as short as possible. The narrowing of the throat height is determined by a polishing amount from the air bearing surface.
Thus, for enhancing the performance of the composite type thin film magnetic head composed of the stacked writing inductive type thin film magnetic head and reading magnetoresistive effective type thin film magnetic head, it is important to balance the writing inductive type thin film magnetic head with the reading magnetoresistive effective type thin film magnetic head.
FIGS. 1-8 shows successive manufacturing steps of a conventional normal composite type thin film magnetic head. In each figures, reference "A" depicts a cross sectional view, taken on a surface perpendicular to an air bearing surface, and reference "B" depicts a cross sectional view, taken on a surface parallel to the air bearing surface.
First of all, as shown in FIG. 1, an insulating layer 2 made of alumina (Al.sub.2 O.sub.3) is formed in a thickness of about 5-10 .mu.m on a substrate 1 made of alumina-titanium-carbon (AlTiC), for example, on which a bottom shielding layer 3 constituting one magnetic shield layer to protect a MR reproducing element from an external magnetic field is formed, of permalloy, in a thickness of 2-3 .mu.m. Then, as shown in FIG. 2, a bottom shield gap layer 4 is sputter-formed, of alumina, in a thickness of about 100-150 .mu.m, and thereafter a magnetoresistive layer 5 constituting the MR reproducing element is formed, of a material having a magnetoresistive effect, in a thickness of several ten nm, and processed into a desired shape with a precise mask alignment. Subsequently, conductive layers 6a and 6b to connect the magnetoresistive element to an external circuit are formed. A top shield gap layer 7 is formed, of alumina, on a thickness of 100-150 nm, and thereafter, a top pole 8 is formed, of permalloy in a thickness of 3 .mu.m. The top pole 8 functions as a top shield to magnetically shield the MR reproducing element as well as the above bottom shield layer 3, but does as a bottom pole of the writing thin film magnetic head importantly, so it is called as a "bottom pole" hereinafter.
Next, as shown in FIG. 3, on the bottom pole 8 is formed, of a non magnetic material, for example, alumina, a write gap layer 9 having a thickness of about 200 nm, on which a magnetic layer is formed of a high saturated magnetic flux density such as permalloy (Ni: 50 wt %, Fe: 50 wt %) or iron nitride (FeN). Then, a top pole 10 is formed into a desired shape through a precise mask alignment. The width W of the pole chip 10 defines the track width. Thus, high surface recording density requires to narrow the width W of the pole chip 10. In this case, a connecting member 11 to magnetically connect the bottom pole 8 and a top pole to be formed later is formed at the same time, which can make easy open a through hole after mechanical polishing or chemical mechanical polishing (CMP).
Then, as shown in FIG. 4, for preventing the broadening of the effective writing track width, that is, for preventing the broadening of the magnetic flux of one pole in writing data, the write gap layer 9 and the bottom pole are etched by ion beam etching such as ion milling to form a trim structure. Thereafter, an insulating layer 12 is formed, of alumina, in a thickness of 3 .mu.m, and is flattened by CMP so as to have the same level surface as the pole chip 10.
Thereafter, as shown in FIG. 5, a first thin film coil 13 is formed, of Cu, for example, so as to be supported in insulated separation by an insulating layer 14, the surface of which is flattened. Then, a second thin film coil 15 is formed on the surface of the insulating layer 14 so as to be supported in insulated separation by an insulating layer 16.
The thus obtained assembly is fired at 250.degree. C., for example, to flatten the surface of the insulating layer 16 to support the second thin film coil 15. Thereafter, as shown in FIG. 6, a top pole 17 made of permalloy is selectively formed alongside a desired pattern, in a thickness of 3 .mu.m, on the pole chip 10 and the insulating layers 14, 16, and an overcoat layer 18 is formed, of alumina, on the surface over the thus obtained assembly.
Finally, the sides of the assembly are polished to form an air bearing surface (ABS) 19 opposing to a magnetic recording medium. In the forming process of the air bearing surface 19, the magnetoresistive layer 5 is polished, too and thereby, a MR reproducing element 20 is obtained. In this way, the above throat height TH and MR height MRH are determined.
In a real thin film magnetic head, pads to electrically connect the thin film coils 13, 15 and the MR reproducing element 20 are formed, but omitted in the figures.
FIG. 7 is a plan view, as shown in FIG. 4, showing the state in which the pole chip 10 and the connecting member 11 are formed on the write gap layer 9 so as to have the same surface level as that of the insulating layer 12. In the figure, the top pole 17 to be formed later is denoted as a virtual line. The pole chip 10 extends from the end of the air bearing surface to the standard position TH.sub.0 as throat height=0, and the magnetic pole portion of the top pole 17 is formed so as to cover the pole chip entirely.
FIG. 8 is a plan view showing the state in which the overcoat layer 18 is removed from the complete composite type thin film magnetic head shown in FIG. 6. As is shown in the figure, the width W of the magnetic pole portion in the pole chip 10 and top pole 17 is narrowed. Then, since the track width in recording into a magnetic recording medium is determined by the width W, the width is narrowed as small as possible for realizing a high surface recording density. Hereupon, for simplifying the figure, the thin film coils 13 and 15 are shown in concentric circle.
In the past, a special problem in forming a thin film magnetic head is a difficulty of forming, finely, a coil convex portion covered with a photoresist insulating layer, particularly a top pole alongside its slope (Apex) after forming the thin film coil.
Conventionally, the top pole is formed as follows: A magnetic material such as permalloy is plated on a coil convex portion having a height of about 7-10 .mu.m. Then, a photoresist is applied in a thickness of 3-4 .mu.m, and thereafter, is processed into a given pattern by a photolithography technique. If the pattern resist on the heap-like coil convex portion requires a minimum thickness of 3 .mu.m, the photoresist is applied in a thickness of 8-10 .mu.m in the bottom part of the slope.
Moreover, the top pole formed on the surface of the coil convex portion having a vertical interval of about 10 .mu.m and the flattened write gap layer is required to be processed finely as the track width is narrowed. However, if a narrowed pattern having a width of about 1 .mu.m is formed from a thick photoresist film having a thickness of 8-10 .mu.m, the pattern breaks due to the reflected light from the light used in exposing the photoresist film and the resolution is degraded due to the large thickness of the photoresist. Thus, it is very difficult to pattern a narrowed top pole to form a narrowed track precisely.
Accordingly, for writing data with a recording head having a pole chip whereby a narrowed track width can be formed as the above conventional example, a two-divided structure-thin film magnetic head, formed by forming the pole chip and thereafter, connecting a top pole to the pole chip, is proposed. That is, the two-divided structure-thin film magnetic head has a pole chip to determine a track width and a top pole to induce a magnetic flux.
As mentioned above, however, the thin film magnetic head including the pole chip and the top pole has the following problems:
(1) In the case of requiring a track width of submicron order, particularly about 0.5 .mu.m, the magnetic pole portion of the top pole as well as that of the pole chip is required to be micro-processed in submicron order, which has difficulty being realized by the conventional photolithography. PA0 (2) Since the relative position of the pole chip 9 and the top pole 17 is determined by an alignment of photolithography, as is viewed from the air bearing surface, the center line of the pole chip can shift from the center line of the top pole. Consequently, the magnetic flux leaked from the top pole may record data, and thereby, the effective track width become large, resulting in the side write of recording data in the adjacent track mistakenly. For preventing the side write, the track width is required to be large, so that a high surface recording density can not be obtained.
For ironing out the side write, a thin film magnetic head in which a forefront of a top pole is receded from an air bearing surface is suggested, and an example of the thin film head is described in Kokai publication No. 10-55516. Although in the conventional thin film magnetic head, the top pole is formed in a given pattern by photolithography, the photolithography has difficulty receding the forefront of the top pole from the air bearing surface by a given distance precisely in forming the magnetic pole portion of the top pole having a submicron order width. Particularly, it is very difficult to micro-process the forefront of the top pole without the fluctuation of the dimension and shape of the pole chip, and besides, the micro-processing degrades the characteristics and process yield of the thin film magnetic head.
Although in the thin film magnetic head in which the forefront of the top pole is receded from the air bearing surface, the part in between the forefront of the top pole and the air bearing surface is embedded with an overcoat layer, the overcoat layer made of alumina is peeled off in the polishing process to form the air bearing surface because the forefront of the magnetic pole portion of the top pole is almost perpendicular to the surface of the pole chip.
Moreover, in the thin film magnetic head having the pole chip and the top pole, the opposite surface of the pole chip to the air bearing surface has to be a standard position of throat height=0. Thus, the pole chip can not extended backward beyond the standard position, and thereby, the contacting area between the pole chip and the magnetic pole portion of the top pole is small, resulting in the saturation of the magnetic flux in the contacting area.